The persistent high prevalence of HIV infection in many parts ofthe U.S. and other countries, worsening HIV disparities, and the increasing complexity of the medical and social conditions confronted by individuals living with HIV/AIDS as survival improves and infected individuals age, all underscore the need for interdisciplinary biomedical, clinical, and socio-behavioral research that addresses the prevention and treatment spectrum. These developments in the epidemic, together with the new emphasis on treatment as prevention, accentuate the need to combine social and behavioral research with HIV clinical and health systems research to identify and implement high impact and sustainable approaches to HIV prevention and treatment. In the past several years HIV researchers have identified promising HIV prevention strategies for reducing the incidence of new infections that focus on HIV-infected individuals. Emerging evidence on the benefit of antiretroviral treatment in reducing transmission, as well as reducing HIV morbidity and mortality, has significantly altered the way we think about HIV prevention and treatment. Global and U.S. based studies suggest that identifying people with HIV infection early on, linking them to care, and increasing adherence to antiretroviral therapy can reduce the risk of infecting others while improving health outcomes for those who are infected. Clinical and health services and systems research are thus increasingly focusing on HIV prevention! The emergence of non-vaccine interventions such as pre-exposure prophylaxis (PrEP) for the prevention of HIV infection, data on the impact of microbicides, and studies of approaches to clinical ? management of HIV and comorbid conditions to improve outcomes all emphasize the need to consider the role of medical care when trying to-optimize prevention efforts.? All of these discoveries and trends provide a greater impetus to learn about the most effective and efficient ways to improve identification of the undiagnosed, identify individuals earlier in their infection, link and retain them in care, maintain viral suppression, screen and treat comorbid disease, and improve health outcomes. Settings where individuals receive care increasingly are a critical focus when developing prevention strategies, and improvements in care have the potential to alter the course of the epidemic, although there are formidable obstacles to full and rapid implementation of the goals of the national and global HIV/AIDS strategies. The 2011 lOM report on HIV screening and access to care reviews many ofthe barriers that could impede implementation ofthe test and treat approach in the U.S. including deficiencies in capacity to scale up routine testing and early, sustained access to care and the need for coordinated care and integrated delivery systems. Likewise, the Global AIDS plan calls for unconventional and multi-level approaches and innovative solutions to overcome deficiencies in the current delivery of HIV services in resource poor settings. The CHSR Core was founded on the recognition that there are many unrealized opportunities for HIV prevention in clinical settings as well as opportunities to improve health outcomes and reduce HIV disparities. With the advent of the test-and-treat strategy, and the increasing importance of treatment as prevention, the work ofthe CHSR Core is ever more vital to CIRA's impact on the course ofthe epidemic in the U.S. and globally. Understanding the factors that facilitate or impede the implementation of prevention and treatment programs is a central focus of health services research, thus CHSR will play a critical role in realizing CIRA's new emphases on implementation research, and on building research expertise in small urban areas with high HIV prevalence. Composed of clinicians and researchers from diverse disciplines, the Core is uniquely positioned to bridge the biomedical, clinical, health services, and social-behavioral sciences and to promote and facilitate research to improve the prevention and treatment of comorbid conditions among those with or at risk for HIV/AIDS.